PhD Thesis Defence: Mr. Sandeep Tripathi (22/01/24)

Thesis title:

“Thermoplastic” epoxy designed using vitrimer chemistries

Faculty advisor(s):

Prof. Suryasarathi Bose


22nd January, 2024 (Monday), 02:30 PM (India Standard Time)


Online, Department of Materials Engineering


Globally, 70 million tons of epoxy thermosets are manufactured at a perplexing rate which constitutes approximately a quarter of polymer generation by weight. A thermosetting polymercontains a permanent crosslinked network and is one that undergoes degradation without goingthrough fluid state on heating at high temperatures. This in turn dramatically reduces its durability and longevitywhich persuades the requirement of disposing it in landfillsor incineration leadingto environmental pollutionand difficulty in waste management. Unfortunately, this disposal strategy attributes to the rising dangers and concerns for the environment. Epoxy resins are thermosetting polymeric liquids that are viscous and contain epoxides in their chemical structure. Its properties such as light weight, good adhesion, high moisture and chemical resistance, strong durability at high and low temperatures, low shrinkage and great mechanical properties makes it a desirablematrix use in various applications. There is an increasing need for sustainable polymeric materials that not only exceed strict performance requirements but also have the capacity to be recycledand reprocessed in severaldifferent industries, including aerospace, automotive, transportation, and medical. In recent times, the emergence of vitrimers with self-healing technology has sparked significant interest in exploring innovative approaches for self-healing on the interface as well as bulk phenomena. This area shows great promise and potentialfor advancements in various fields. Vitrimers have become a potential class of polymers because of these demands. Unlike other materials, vitrimershave dynamic covalentcrosslinks that enable temperature-dependent exchange kinetics. This property enables vitrimers to behave like thermoplastics that can be reprocessed at high temperatures alongwith retaining and accomplishing the desired resistance to chemical and mechanical stress comparable to thermosets at the application temperatures. These unconventional polymer networks rely on dynamic bonds that can react reversibly, namely covalentadaptable networks (CANs).The CANs could release stress from deformation, allowing the crosslinked polymers to be reprocessed, reshaped,and recycled. The heavy amounts of stress, force, high temperature, and pressure in various applications that the material is subjected to results in cracks and fractures and consequently the life of the materialis shortened. In this thesis, we have successfully synthesized single, dual and tripledynamic CANs to design epoxy based Vitrimer. The resulting Vitrimer cure within 2 hours in contrast to traditional epoxies which take typically 12-14 hours to completely cure. The resulting epoxy vitrimers exhibited high tensile strength, exceptionally high Tg, fast stress relaxation and high an activation energy. Due to the pre-installed CAN, they show flow induced activation and can change network topology triggered by temperature. Such materials could widely be used in various applications in automobile, aerospace technology etc where frequent maintenance is required and in addition can be recycled due to the presence of dynamic bonds. This thesis systematically evaluates the self-healing, reusability and re-processability, triggered by the exchangeable bonds, in the epoxy Vitrimer.